This invention relates to processes for preparing 1H-imidazo[4,5-c]pyridin-4-amines and to intermediates for use in preparing 1H-imidazo[4,5-c]pyridin-4-amines.
Certain antiviral immunomodulator 1H-imidazo[4,5-c]pyridin-4-amines and methods for their preparation are known and disclosed. For example, U.S. Pat. No. 5,494,916 (Lindstrom et al.), incorporated herein by reference, discloses a method involving the steps of forming a 1H-imidazo[4,5-c]pyridine substituted at the 4 position with a hydrogenolyzable amine and hydrogenolyzing using known catalytic hydrogenation conditions to provide the 4-amino compound.
Methods of making certain 1H-imidazo[4,5-c]quinolin-4-amines are also known. For example U.S. Pat. Nos. 4,689,338 and 4,929,624 (Gerster) disclose a method involving the step of heating the corresponding 4-chloro compound in the presence of ammonium hydroxide or ammonia under pressure to provide the 4-amino compound. U.S. Pat. No. 4,988,815 (Andre et al.) discloses a process involving amination of the 4-position of a 3-nitro-2,4-dichloroquinoline. This process too involves as a final step the reaction of animonia with 4-chloro-1H-imidazo[4,5-c]quinoline. U.S. Pat. No. 5,175,296 (Gerster) discloses a process involving the reaction of a 1H-imidazo[4,5-c]quinoline 5N-oxide with an organic isocyanate and hydrolyzing the product to provide the 4-amino compound. U.S. Pat. No. 5,367,076 (Gerster) discloses a process involving the reaction of a 1H-imidazo[4,5-c]quinoline 5N-oxide with an acylating agent and reacting the product with an aminating agent to provide the 4-amino compound. U.S. Pat. No. 5,395,937 (Nikolaides) discloses a process involving amination of the 4-position of a 3-nitroquinolin-2,4-disulfonate with a substituted amine. The final step of the process involves hydrogenolysis to provide the 4-amino compound. U.S. Pat. No. 5,741,908 (Gerster et al.) discloses a process involving the reaction of a 6H-imidazo[4,5-c]tetrazolo[1,5-a] quinoline with triphenylphosphine to provide an N-triphenylphosphinyl-1H-imidazo[4,5-c]quinolin-4-amine and a subsequent hydrolysis to provide a 1H-imidazo[4,5-c]quinoline-4-amine.
Methods of making certain 1-(substituted aryl)alkyl-1H-imidazo[4,5-c]quinolin-4-amines, 6,7,8,9-tetrahydro-1H-imidazo[4,5-c]quinolin-4-amines, 1,6,7,8-tetrahydrocyclopenta[b]imidazo[4,5-d]pyridin-4-amines, and 1,6,7,8,9,10-hexahydrocyclohepta[b]imidazo[4,5-d]pyridin-4-amines are also known. Japanese Unexamined Patent Publication No. 11-80156 discloses a process involving the reaction of the corresponding 4-chloro compound and phenol with an alkali to form the corresponding 4-phenoxy compound, which is reacted with ammonium acetate to provide the 4-amino compound.
Despite these developments in methods for making certain imidazoquinolin- and imidazopyridin-4-amines, there is a continuing need for useful, alternative processes and intermediates for preparing imidazo[4,5-c]pyridin4-amines.
This invention provides a process (I) for preparing a 1H-imidazo[4,5-c]pyridin-4-amine compound of Formula I 
or a pharmaceutically acceptable salt thereof wherein
R1 is selected from hydrogen; CHRxRy wherein Rx is hydrogen and Ry is selected from alkyl or cyclic alkyl containing one to ten carbon atoms, straight chain or branched chain alkenyl containing two to ten carbon atoms, hydroxyalkyl containing one to six carbon atoms, alkoxyalkyl wherein the alkoxy moiety contains one to four carbon atoms and the alkyl moiety contains one to six carbon atoms, benzyl, and phenylethyl; and xe2x80x94Cxe2x95x90CRzRz wherein each Rz is independently alkyl or cyclic alkyl of one to six carbon atoms;
R2 is selected from hydrogen; alkyl containing one to eight carbon atoms; hydroxyalkyl containing one to six carbon atoms; alkoxyalkyl wherein the alkoxy moiety contains one to four carbon atoms and the alkyl moiety contains one to six carbon atoms; benzyl; phenylethyl; and phenyl; the benzyl, phenylethyl, or phenyl substituent being optionally substituted on the benzene ring by a moiety selected from methyl, methoxy, and halogen; and morpholinoalkyl wherein the alkyl moiety contains one to four carbon atoms;
R3 and R4 are independently selected from hydrogen and alkyl of one to five carbon atoms; which process comprises the steps of:
(1) providing a compound of Formula II 
wherein R3 and R4 are as described above;
(2) reacting the compound of the Formula II with a chlorinating agent to provide a compound of Formula III 
(3) reacting the compound of the Formula III with a compound of formula R1NH2, wherein R1 is as defined above, to provide a compound of Formula IV 
(4) reacting the compound of the Formula IV with an alkali metal phenoxide to provide a compound of Formula V 
(5) reducing the compound of the Formula V to provide a compound of Formula VI 
(6) reacting the compound of the Formula VI with a carboxylic acid of the formula R2CO2H; an equivalent thereof selected from the corresponding acyl halide, R2C(O-alkyl)3, and R2C(O-alkyl)2(O(Oxe2x95x90)C-alkyl); or a mixture thereof, wherein R2 is as defined above and each alkyl contains 1 to 8 carbon atoms, to provide a compound of Formula VIII 
(7) reacting the compound of the Formula VIII with an aminating agent to provide the compound of the Formula I.
In some embodiments, in step (6) the compound of the Formula VI is reacted with the carboxylic acid of the formula R2CO2H; an equivalent thereof selected from the corresponding acyl halide, R2C(O-alkyl)3, and R2C(O-alkyl)2(O(Oxe2x95x90)C-alkyl); or a mixture thereof; in the presence of cyclization conditions to provide a compound of the Formula VIII.
In some embodiments, step (6) includes the steps of:
(6a) reacting the compound of the Formula VI with a carboxylic acid of the formula R2CO2H or the corresponding acyl halide to provide a compound of Formula VII 
(6b) subjecting the compound of the Formula VII to cyclization conditions, during step (6a) or subsequent to the completion of step (6a), to provide a compound of the Formula VIII.
In some embodiments the above process (I) further comprises the step of isolating the compound of the Formula I or a pharmaceutically acceptable salt thereof.
In another embodiment this invention provides a process (II) for preparing a 1H-imidazo[4,5-c]pyridin-4-amine compound of the Formula I 
or a pharmaceutically acceptable salt thereof wherein
R1 is selected from hydrogen; CHRxRy wherein Rx is hydrogen and Ry is selected from alkyl or cyclic alkyl containing one to ten carbon atoms, straight chain or branched chain alkenyl containing two to ten carbon atoms, hydroxyalkyl containing one to six carbon atoms, alkoxyalkyl wherein the alkoxy moiety contains one to four carbon atoms and the alkyl moiety contains one to six carbon atoms, benzyl, and phenylethyl; and xe2x80x94Cxe2x95x90CRzRz wherein each Rz is independently alkyl or cyclic alkyl of one to six carbon atoms;
R2 is selected from hydrogen; alkyl containing one to eight carbon atoms; hydroxyalkyl containing one to six carbon atoms; alkoxyalkyl wherein the alkoxy moiety contains one to four carbon atoms and the alkyl moiety contains one to six carbon atoms; benzyl; phenylethyl; and phenyl; the benzyl, phenylethyl, or phenyl substituent being optionally substituted on the benzene ring by a moiety selected from methyl, methoxy, and halogen; and morpholinoalkyl wherein the alkyl moiety contains one to four carbon atoms;
R3 and R4 are independently selected from hydrogen and alkyl of one to five carbon atoms; which process comprises the steps of:
(1) providing a compound of Formula II 
wherein R3 and R4 are as described above;
(2) reacting the compound of the Formula II with a chlorinating agent to provide a compound of Formula III 
(3) reacting the compound of the Formula III with a compound of formula R1NH2, wherein R1 is as defined above, to provide a compound of Formula IV 
(4) reducing the compound of the Formula IV to provide a compound of Formula IX 
(5) reacting the compound of the Formula IX with a carboxylic acid of the formula R2CO2H; an equivalent thereof selected from the corresponding acyl halide, R2C(O-alkyl)3, and R2C(O-alkyl)2(O(Oxe2x95x90)C-alkyl); or a mixture thereof, wherein R2 is as defined above and each alkyl contains 1 to 8 carbon atoms to provide a compound of Formula XI 
(6) reacting the compound of the Formula XI with an alkali metal phenoxide to provide a compound of Formula VIII 
(7) reacting the compound of the Formula VIII with an aminating agent to provide a compound of the Formula I.
In some embodiments, in step (5) the compound of the Formula IX is reacted with the carboxylic acid of the formula R2CO2H; an equivalent thereof selected from the corresponding acyl halide, R2C(O-alkyl)3, and R2C(O-alkyl)2(O(Oxe2x95x90)C-alkyl); or a mixture thereof; in the presence of cyclization conditions, to provide a compound of the Formula XI.
In some embodiments, step (5) includes the steps of:
(5a) reacting the compound of the Formula IX with a carboxylic acid of the formula R2CO2H or the corresponding acyl halide to provide a compound of Formula X 
(5b) subjecting the compound of the Formula X to cyclization conditions, during step (5a) or subsequent to the completion of step (5a) to provide a compound of the Formula XI.
In some embodiments the above process (II) further comprises the step of isolating the compound of Formula I or a pharmaceutically acceptable salt thereof.
In another aspect this invention also provides compounds of the formulae 
and pharmaceutically acceptable salts thereof.
As used herein, xe2x80x9calkylxe2x80x9d includes straight chain alkyl and branched chain alkyl wherein the alkyl is either unsubstituted or substituted. For example, the alkyl portion of substituted alkyls such as hydroxyalkyl and alkoxyalkyl includes straight chain alkyl and branched chain alkyl.
Reaction Scheme I illustrates a process of the invention where R1, R2, R3, and R4 are as defined above, and Ph is phenyl.
In the first step of Reaction Scheme I a 2,4dihydroxy-3-nitropyridine of Formula II is provided. Many 2,4-dihydroxy-3-nitropyridines of Formula II are known and others can be readily prepared using known synthetic methods, see for example, Lindstrom et al., U.S. Pat. No. 5,446,153 and the documents cited therein. In some embodiments, R3 and R4 in Formula II are independently hydrogen or methyl, and in others R3 and R4 are both methyl.
In step (2) of Reaction Scheme I a 2,4dihydroxy-3-nitropyridine of Formula II is chlorinated using conventional chlorinating agents to provide a 2,4-dichloro-3-nitropyridine of Formula III. Examples of chlorinating agents include, but are not limited to, phosphorus oxychloride, thionyl chloride, phosgene, oxalyl chloride, and phosphorus pentachloride. In a preferred embodiment, the chlorinating agent is phosphorus oxychloride. The chlorinating agent may be used in the absence or presence of an inert solvent such as N,N-dimethylformamide or methylene chloride and at temperatures up to the reflux temperature. For example, a compound of Formula II is combined with phosphorous oxychloride and heated. The product can be isolated from the reaction mixture using conventional methods.
In step (3) of Reaction Scheme I a 2,4dichloro-3-nitropyridine of Formula III is reacted with an amine compound of formula R1NH2 to provide a 2-chloro-3-nitropyridine of Formula IV. In certain embodiments the compound of formula R1NH2 is selected from 2-hydroxy-2-methylpropylamine and 2-methylpropylamine. The reaction may be carried out in an inert solvent such as N,N-dimethylformamide or methylene chloride in the presence or in the absence of a base such as triethylamine at a temperature up to the reflux temperature of the solvent. For example, the reaction is carried out by adding the amine to a solution of a compound of Formula III in a suitable solvent such as N,N-dimethylformamide in the presence of a tertiary amine such as triethylamine. The product can be isolated from the reaction mixture using conventional methods.
In step (4) of Reaction Scheme I a 2-chloro-3-nitropyridine of Formula IV is reacted with an alkali metal phenoxide to provide a 3-nitro-2-phenoxypyridine of Formula V. For example, phenol is reacted with sodium hydride in a suitable solvent such as diglyme to form the sodium phenoxide, and the sodium phenoxide is then reacted at an elevated temperature with a compound of Formula IV. The product can be isolated from the reaction mixture using conventional methods.
In step (5) of Reaction Scheme I the compound (a 3-nitro-2-phenoxypyridine of Formula V) provided by step (4) is reduced to provide a 3-amino-2-phenoxypyridine of Formula VI. Preferably, the reduction is carried out using a conventional heterogeneous hydrogenation catalyst. The catalyst may be selected from, for example, platinum on carbon and palladium on carbon. The reaction can conveniently be carried out on a Parr apparatus in a suitable solvent such as isopropyl alcohol or toluene. Alternatively, Ni2B can be generated in situ from sodium borohydride and NiCl2 in the presence of methanol. The compound of Formula V is added to the reducing agent solution to effect reduction of the nitro group. When the compound of Formula V contains an alkenylene moiety, the Ni2B reducing agent can be used without reducing the alkenylene moiety. The product can be isolated from the reaction mixture using conventional methods.
In step (6) of Reaction Scheme I a 3-amino-2-phenoxypyridine of Formula VI is reacted with a carboxylic acid of the formula R2CO2H, an equivalent thereof, or a mixture thereof, in the presence of cyclization conditions or followed by cyclization conditions to provide a 4-phenoxy-1H imidazo[4,5-c]pyridine of Formula VIII. Suitable equivalents to the carboxylic acid include compounds of the formula R2C(O-alkyl)3, 1,1-dialkoxyalkyl alkanoates (R2C(O-alkyl)2(OOC-alkyl)), corresponding acyl halides, and mixtures thereof, wherein R2 is as defined above and each alkyl contains 1 to 8 carbon atoms. The carboxylic acid or equivalent is selected such that it will provide the desired R2 substituent in the compound of Formula VIII. For example, triethyl orthoformate will provide a compound where R2 is hydrogen, and trimethyl orthovalerate will provide a compound where R2 is butyl. In certain embodiments, R2 is ethoxymethyl, and in other embodiments, R2 is ethoxymethyl when R1 is selected from 2-hydroxy-2-methylpropyl and 2-methylpropyl. In some embodiments, R2 is ethoxymethyl when R1 is selected from 2-hydroxy-2-methylpropyl and 2-methylpropyl, and R3 and R4 are independently hydrogen and methyl. The reaction can be run in the absence of solvent or in an inert solvent such as, for example, toluene, dichloromethane, acetonitrile, or pyridine. The product or a pharmaceutically acceptable salt thereof can be isolated from the reaction mixture using conventional methods.
The cyclization conditions include heating to an elevated temperature, such as a reflux temperature, sufficient to drive off any alcohol or water formed as a by-product of the reaction. Optionally, the presence of a catalyst such as pyridine hydrochloride can be included in the cyclization conditions. The cyclization reaction can be run in the absence of a solvent or in an inert solvent such as toluene, pyridine, or other solvent, preferably, having a boiling point of at least about 100xc2x0 C.
In some embodiments, step (6) can be carried out by using steps (6a) and (6b) of Reaction Scheme I. In step (6a) a compound of the Formula VI is reacted with a carboxylic acid of the formula R2CO2H or the corresponding acyl halide, such as R2C(O)Cl or R2C(O)Br, wherein R2 is as defined above, to provide an N-(4-amino-2-phenoxypyridin-3-yl)amide of Formula VII. The reaction can be run by adding the carboxylic acid, corresponding acyl halide, or mixture thereof to the compound of Formula VI dissolved in an inert solvent such as toluene, acetonitrile, pyridine or dichloromethane. The reaction can be carried out at or below ambient temperature, for example, in the range of 0 to 30xc2x0 C. The product can be isolated from the reaction mixture using conventional methods.
In step (6b) the N-(4-amino-2-phenoxypyridin-3-yl)amidc of Formula VII is cyclized to provide a 4-phenoxy-1H imidazo[4,5-c]pyridine of Formula VIII. The cyclization can be carried out at an elevated temperature, such as a reflux temperature, sufficient to drive off any water formed as a by-product of the reaction. Optionally a catalyst such as pyridine hydrochloride can be included. The reaction can be run in the absence of solvent or in an inert solvent such as toluene, pyridine, or other solvents, preferably having a boiling point of at least about 100xc2x0 C. Step (6b) may be run concurrently with step (6a) without first isolating the product of step (6a). The product can be isolated from the reaction mixture using conventional methods. In one embodiment, the acyl halide is ethoxyacetyl chloride, and the cyclization conditions include an elevated temperature and the presence of pyridine, preferably with pyridine hydrochloride catalyst, during the reaction of the ethoxyacetyl chloride with the compound of Formula VI.
In step (7) of Reaction Scheme I a 4-phenoxy-1H-imidazo[4,5-c]pyridine of Formula VIII is aminated to provide a 1H-imidazo[4,5-c]pyridine-4-amine of Formula I. In one embodiment, the aminating agent is ammonium acetate. The reaction can be carried out by combining a compound of Formula VIII with ammonium acetate and heating, for example, in a sealed container with heating at about 150xc2x0 C. The product or a pharmaceutically acceptable salt thereof can be isolated using conventional methods. 
In certain embodiments of the above process (I) R1 is selected from 2-hydroxy-2-methylpropyl and 2-methylpropyl.
In certain embodiments of the above process (I) R2 is ethoxymethyl.
In certain embodiments of the above process (I) R3 and R4 are independently hydrogen or methyl.
In other embodiments of the above process (I) R3 and R4 are both methyl.
In some embodiments of the above process (I) R1 is selected from 2-hydroxy-2-methylpropyl and 2-methylpropyl, and R2 is ethoxymethyl.
In some embodiments of the above process (I) R1 is selected from 2-hydroxy-2-methylpropyl and 2-methylpropyl, R2 is ethoxymethyl, and R3 and R4 are independently hydrogen or methyl.
In some embodiments of the above process (I), in step (6a) the carboxylic acid equivalent is the corresponding acyl halide of R2CO2H, and in step (6b) the cyclization conditions include heating to an elevated temperature and a condition selected from the presence of pyridine, and the presence of pyridine with pyridine hydrochloride.
In one embodiment of the above process (I), the acyl halide is ethoxyacetyl chloride, and the cyclization conditions include an elevated temperature and the presence of pyridine during step (6a).
In another embodiment of the above process (I), the alkali metal phenoxide is sodium phenoxide.
In another embodiment of the above process (I), the chlorinating agent is phosphorus oxychloride.
In another embodiment of the above process (I), the compound of the formula R1NH2 is selected from 2-hydroxy-2-methylpropylamine and 2-methylpropylamine.
In another embodiment of the above process (I), in step (5) the compound of Formula V is reduced with a heterogeneous hydrogenation catalyst. For example, the heterogeneous hydrogenation catalyst is selected from platinum on carbon and palladium on carbon.
In another embodiment of the above process (I), the aminating agent is ammonium acetate.
In some embodiments of the above process (I) the compound of Formula I is selected from 
and pharmaceutically acceptable salts thereof.
Reaction Scheme II also illustrates a process of the invention where R1, R2, R3, and R4 are as defined above, and Ph is phenyl.
In the first step of Reaction Scheme II a 2,4-dihydroxy-3-nitropyridine of Formula II is provided. Many 2,4-dihydroxy-3-nitropyridines of Formula II are known and others can be readily prepared using known synthetic methods, see for example, Lindstrom et al., U.S. Pat. No. 5,446,153 and the documents cited therein. In some embodiments, R3 and R4 of Formula II are independently hydrogen or methyl, and in others R3 and R4 are both methyl.
In step (2) of Reaction Scheme II a 2,4-dihydroxy-3-nitropyridine of Formula II is chlorinated using conventional chlorinating agents to provide a 2,4-dichloro-3-nitropyridine of Formula III. Examples of chlorinating agents include, but are not limited to, phosphorus oxychloride, thionyl chloride, phosgene, oxalyl chloride, and phosphorus pentachloride. Preferably the chlorinating agent is phosphorus oxychloride. The chlorinating agent may be used in the absence or presence of an inert solvent such as N,N-dimethylformamide or dichloromethane and at temperatures up to the reflux temperature. For example, a compound of Formula II is combined with phosphorous oxychloride and heated. The product can be isolated from the reaction mixture using conventional methods.
In step (3) of Reaction Scheme II a 2,4-dichloro-3-nitropyridine of Formula III is reacted with an amine compound of formula R1NH2 to provide a 2-chloro-3-nitropyridine of Formula IV. In some embodiments, the compound of formula R1NH2 is selected from 2-hydroxy-2-methylpropylamine and 2-methylpropylamine. The reaction may be carried out in an inert solvent such as N,N-dimethylformamide or dichloromethane in the presence or in the absence of a base such as triethylamine at a temperature up to the reflux temperature of the solvent. For example, the reaction is carried out by adding the amine to a solution of a compound of Formula III in a suitable solvent such as N,N-dimethylformamide in the presence of a tertiary amine such as triethyl amine. The product can be isolated from the reaction mixture using conventional methods.
In step (4) of Reaction Scheme II the compound (a 2-chloro-3-nitropyridine of Formula IV) provided by step (3) is reduced to provide a 3-amino-2-chloropyridine of Formula IX. Preferably, the reduction is carried out using a conventional heterogeneous hydrogenation catalyst, for example, platinum on carbon. The reaction can conveniently be carried out on a Parr apparatus in a suitable solvent such as isopropyl alcohol or toluene. Alternatively, Ni2B can be generated in situ from sodium borohydride and NiCl2 in the presence of methanol. The compound of Formula V is added to the reducing agent solution to effect reduction of the nitro group. When the compound of Formula V contains an alkenylene moiety, the Ni2B reducing agent can be used without reducing the alkenylene moiety. The product can be isolated from the reaction mixture using conventional methods.
In step (5) of Reaction Scheme II a 3-amino-2-chloropyridine of Formula IX is reacted with a carboxylic acid of the formula R2CO2H, an equivalent thereof, or a mixture thereof, in the presence of cyclization conditions or followed by cyclization conditions to provide a 4-chloro-1H imidazo[4,5-c]pyridine of Formula XI. Suitable equivalents to the carboxylic acid include compounds of the formula R2C(O-alkyl)3, 1,1,-dialkoxyalkyl alkanoates (R2C(O-alkyl)2(OOC-alkyl)), corresponding acyl halides, and mixtures thereof, wherein R2 is as defined above and each alkyl contains 1 to 8 carbon atoms. The carboxylic acid or equivalent is selected such that it will provide the desired R2 substituent in the compound of Formula XI. For example, triethyl orthoformate will provide a compound where R2 is hydrogen, and trimethyl orthovalerate will provide a compound where R2 is butyl. In certain embodiments, R2 is ethoxymethyl, and in other embodiments, R2 is ethoxymethyl when R1 is selected from 2-hydroxy-2-methylpropyl and 2-methylpropyl. In some embodiments, R2 is ethoxymethyl when R1 is selected from 2-hydroxy-2-methylpropyl and 2-methylpropyl, and R3 and R4 are independently hydrogen and methyl. The reaction can be run in the absence of solvent or in an inert solvent such as, for example, toluene, dichloromethane, acetonitrile, or pyridine. The product or a pharmaceutically acceptable salt thereof can be isolated from the reaction mixture using conventional methods.
The cyclization conditions include heating to an elevated temperature, such as a reflux temperature, sufficient to drive off any alcohol or water formed as a byproduct of the reaction. Optionally, the presence of a chlorinating agent such as phosphorus oxychloride can be included in the cyclization conditions. The reaction can be run in the absence of solvent or in an inert solvent such as toluene or other solvents, preferably, have a boiling point of at least about 100xc2x0 C.
In some embodiments step (5) can be carried out by using steps (5a) and (5b) of Reaction Scheme II. In step (5a) a compound of the Formula IX is reacted with a carboxylic acid of the formula R2CO2H or the corresponding acyl halide, such as R2C(O)Cl or R2C(O)Br, wherein R2 is as defined above, to provide an N-(4-amino-2-chloropyridin-3-yl)amide of Formula X. The reaction can be run by adding the carboxylic acid, corresponding acyl halide, or mixture thereof to the compound of Formula IX dissolved in an inert solvent such as toluene, acetonitrile, pyridine or dichloromethane. The reaction can be carried out at or below ambient temperature, for example, in the range of 0 to 30xc2x0 C. Optionally, a tertiary amine, for example triethylamine, is included. The product can be isolated from the reaction mixture using conventional methods.
In step (5b) the N-(4-amino-2-chloropyridin-3-yl)amide of Formula X is cyclized to provide a 4-chloro-1H imidazo[4,5-c]pyridine of Formula XI. The cyclization can be carried out at an elevated temperature, such as a reflux temperature or about 100xc2x0 C. to about 150xc2x0 C., for example about 110xc2x0 C. to about 135xc2x0 C., sufficient to drive off any water formed as a by-product of the reaction. The reaction may be carried out in an inert solvent such as toluene, optionally in the presence of phosphorus oxychloride. Step (5b) may be run concurrently with step (5a) without first isolating the product of step (5a). The product can be isolated from the reaction mixture using conventional methods. In one embodiment, the acyl halide is ethoxyacetyl chloride, and the cyclization conditions include an elevated temperature and the presence of phosphorus oxychloride.
In step (6) of Reaction Scheme II a 4-chloro-1H imidazo[4,5-c]pyridine of Formula XI is reacted with an alkali metal phenoxide to provide a 4-phenoxy-1H-imidazo[4,5-c]pyridine of Formula VIII. For example, phenol is reacted with sodium hydride in a suitable solvent such as diglyme to form sodium phenoxide, and the sodium phenoxide is then reacted at an elevated temperature with a compound of Formula XI. The product can be isolated from the reaction mixture using conventional methods.
In step (7) of Reaction Scheme II a 4-phenoxy-1H-imidazo[4,5c]pyridine of Formula VIII is aminated to provide a 1H-imidazo[4,5-c]pyridine-4-amine of Formula I. For example, the aminating agent is ammonium acetate. The reaction can be carried out by combining a compound of Formula VIII with ammonium acetate and beating, for example, in a sealed container with heating at about 150xc2x0 C. The product or a pharmaceutically acceptable salt thereof can be isolated using conventional methods. 
In certain embodiments of the above process (II) R1 is selected from 2-hydroxy-2-methylpropyl and 2-methylpropyl.
In certain embodiments of the above process (II) R2 is ethoxymethyl.
In other embodiments of the above process (II) R3 and R4 are independently hydrogen or methyl.
In other embodiments of the above process (II) R3 and R4 are both methyl.
In some embodiments of the above process (II) R1 is selected from 2-hydroxy-2-methylpropyl and 2-methylpropyl, and R2 is ethoxymethyl.
In some embodiments of the above process (II) R1 is selected from 2-hydroxy-2-methylpropyl and 2-methylpropyl, R2 is ethoxymethyl, and R3 and R4 are independently hydrogen or methyl.
In some embodiments of the above process (II), in step (5a) the carboxylic acid equivalent is the corresponding acyl halide of R2CO2H, and in step (5b) the cyclization conditions include an elevated temperature and the presence of phosphorus oxychloride.
In one embodiment of the above process (II), the acyl halide is ethoxyacetyl chloride, and the cyclization conditions include an elevated temperature and the presence of phosphorus oxychloride.
In another embodiment of the above process (II), the alkali metal phenoxide is sodium phenoxide.
In another embodiment of the above process (II), the chlorinating agent is phosphorus oxychloride.
In other embodiments of the above process (II), the compound of the formula R1NH2 is selected from 2-hydroxy-2-methylpropylamine and 2-methylpropylamine.
In another embodiment of the above process (II), in step (4) the compound of Formula IV is reduced with a heterogeneous hydrogenation catalyst, for example, platinum on carbon.
In another embodiment of the above process (II), the aminating agent is ammonium acetate.
In some embodiments of the above process (II) the compound of Formula I is selected from 
and pharmaceutically acceptable salts thereof.
The invention also provides novel compounds useful as intermediates in the synthesis of the compounds of Formula I. These compounds have the structural Formula VIII 
wherein R1, R2, R3, R4 are as defined above, and Ph is phenyl. Examples of these include compounds of the formulae 
and pharmaceutically acceptable salts thereof.
The invention is further described by the following examples, which are provided for illustration only and are not intended to be limiting in any way.